| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 90 === The structure of the multiuser decorrelating detection is considered for the uplink asynchronous transmission based on the technique of the code-division multiple-access over the time-varying frequency selective fading channel. The aim of the thesis is to validate and evaluate the feasibility and the performance under the third generation mobile communication for this advanced receiver structure. Based on the general system model of the asynchronous transmission, we find that the processing window can be set as two symbol intervals without loss of performance. Some problems may arise for the asynchronous system model when some equivalent spreading codes contain all zeros. We address the problem and prevent the singularity of the direct matrix inversion. By adopting the conjugate gradient algorithm, a kind of iterative algorithm, the singularity problem can be excluded by a unified treatment. This iterative algorithm converges with a small number of iterations and needn’t compute the matrix inversion of high complexity. For the multipath fading environment, it can be combined with the concept of maximum ratio combining straightforwardly.
Under the practical system, we need to estimate the propagation delay and received amplitude. We combine the inaccuracy of channel estimation and the advantage of the decorrelating detector to evaluate the bit error rate in the third generation system with perfect power control over a frequency selective fading channel. Based on the simulation results, it can be shown that the decorrelating detector can be degraded by the erroneous estimation of the delay and amplitude. Moreover, the decorrelating receiver is suitable for the high data rate transmission but in the low rate the performance of the decorrelating detector is inferior to that of the conventional matched filter although using additional computations.
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